This invention relates to pianos.
When a pianist presses upon a piano key, the motion of the key is transmitted to a hammer, which in turn strikes against a tensioned string, to produce sound. The traditional assemblage of levers, pivots, springs and pads that translates key motion into hammer motion, allows the hammer to rebound after striking the string, and further allows for rapid repetition of notes is called a double escapement action.
FIGS. 1/1A through 3/3A demonstrate operation of a prior art double escapement piano action 100. For the purpose of better understanding, with reference to FIGS. 1 and 1A, the following components remain stationary with respect to the piano during a sequence of key depression through hammer strike and return: hammershank flange 134, hammershank flange center pin 136, repetition support center pin 112, key fulcrum 104, key pin 106, drop regulation screw 196, jack let-off button 170 and string 140.
Still referring to FIGS. 1 and 1A, the prior art piano double escapement action 100 is shown in the "at rest"position. Wooden key 102, approximately 15 inches long, is mounted to pivot on felt-covered, wooden fulcrum 104 and brass pin 106 extending through a vertical slot (not visible in the figures) in key 102. Repetition support 110 is mounted for rotation about metal center pin (a fixed pivot point) 112. Two levers are mounted to rotate independently within the repetition assembly: an L-shaped jack 120 (also known as a "fly") mounted to rotate about center pin 121, and repetition lever 123 mounted to rotate about center pin 114. Felt hammer 130 is fixedly mounted at the free end of wooden shank 132 (shown also in FIGS. 7 and 7A), and wooden shank 132 is mounted to rotate about center pin 136, held stationary by flange 134. As the hammer 130 is rotated upwardly, it strikes tensioned piano string 140 to create vibration and sound. Affixed to hammershank 132, between hammer 130 and center pin 136, is buckskin covered cylindrical knuckle 150, engaged upon the top end surface 128 of the upper arm 122 of the jack 120.
The jack 120 is maintained in the "at rest" position shown in FIGS. 1 and 1A by action of a lower end of return spring 160, which bears against the rear surface 129 of the jack, thus urging it to rotate backward (counter-clockwise in the drawings), about center pin 121, until the felt regulating button 162 (mounted on the upper jack arm 128) is brought into contact with the rigid metal spoon 164 (mounted to repetition support 110). The upper end of return spring 160 biases the forward end of repetition lever 123 to rotate upwardly, about center pin 114, until the pad 166, mounted at the opposite end of repetition lever 123 is brought into contact with the repetition support 110.
We refer next to FIGS. 2 and 2A (in which the position of the action 100 in the "at rest" position of FIG. 1A is indicated in dashed line for ease of reference). Upon depression of the key 102 (indicated by arrow 180), repetition support 110 is moved upwardly, to rotate (arrow 182) around center pin 112, thereby actuating the various interengaged elements of the repetition assembly (i.e. repetition support 110, jack 120, repetition lever 123, spring 160, regulating button 162 and spoon 164) and moving the hammer 130 towards striking engagement with the piano string 140. In particular, movement of the jack 120 urges the knuckle 150 upward and to the left (in the drawings), causing the hammershank 132 to rotate about center pin 136, driving the hammer 130, at the free end of the hammershank, upward and to the left, toward the piano string 140 (arrow 184). During movement of the knuckle 150 upward and to the left, the engagement of the knuckle surface with the top end surface 128 of the jack 120 creates excessive friction, which has the recognized consequence of requiring a pianist to apply additional force in order to achieve the desired key depression. In order to minimize this undesirable condition, it has been known to apply lubricant to the opposed top end surface 128 and the surface of knuckle 150, and/or to insert one or more lead counterweights 172 into the front portion of key 102. Approximately midway through full depression of the key 102, the outer end of the lower arm 126 of jack 120 is brought into engagement with stationary let off button 170.
Referring now to FIGS. 3 and 3A (in which the position of the action 100 in FIG. 2A is indicated in dashed line for reference), as key depression continues (indicated by arrow 180), engagement of the jack lower arm 126 with stationary let off button 170 causes the jack 120 to rotate in a clockwise direction, about pin 121. This rotation causes the top end surface 128 of the upper arm 122 of the jack 120 to move forward (to the right in the drawings, indicated by arrow 190), escaping from beneath the surface of the knuckle 150. Movement of the hammer 130 continues upward with rotation of hammershank 132 about pin 136, with the hammer striking the tensioned piano string 140 and then rebounding downward (arrow 192), to lodge against the opposed surface of back check 194.
When the key is released, the elements of the repetition assembly (i.e., repetition support 110, jack 120, repetition lever 123, spring 160, regulating button 162 and spoon 164) return toward the "at rest" position of FIGS. 1 and 1A, by the combined effect of gravity and the force of spring 160 acting through repetition lever 123 against stationary drop regulation screw 196 and knuckle 150. Engagement of hammer 130 with back check 194 holds the hammer in a slightly elevated position, allowing the top end surface 128 of the jack 120 to move quickly, under the urging of spring 160 upon jack 120, back (left in the drawings) to its "at rest" position under knuckle 150, with the regulating button 162 engaged against spoon 164. Upon return of all of the action components to the "at rest" position, a full keystroke is complete.